Auto Zone will read the codes for you! You might invest in a OBD11 code reader, it will pay for itself ! My 2000 S70 GLTSE with a 103K has shown the same code.once cleared it doesn't return for another 1000 miles.It's probably time for a new O2 sensor.

You need to find a local shop with mechanic that knows Volvos. The independents usually have a better idea of what "service" means!

Yes. the code points to the converter but the most likely cause is a leak in the air intake system. Look over intake hoses and vacuum elbows carefully.

p0422 just means 1 of the 02 sensors doesn't like what it smells. codes don't automatically mean a part has gone bad. could be anything from a vacuum leak to a weak o2 sensor. somebody needs to look at it. otherwise, get out the dart board and guess which part it needs. good luck, chuck.